The disclosure of Japanese Patent Application No. 2001-132995 filed on Apr. 27, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a method of operating a vehicular internal combustion engine. In particular, the invention relates to a method of operating a vehicular internal combustion engine that is of an intermittent-operation type, namely, that is designed to be stopped temporarily if a vehicle-operating condition for temporarily stopping the internal combustion engine is fulfilled while the vehicle is running.
2. Description of Related Art
When a vehicular internal combustion engine is started, the amount of fuel is increased temporarily. Such a temporary increase in the amount of fuel at start of an engine aims mainly at temporarily thickening the mixture at start of the engine and thereby improving the startability of the engine. However, some modern vehicles are equipped with an exhaust-gas purification catalyst that captures oxygen upon stoppage of an engine, thus preventing the function of purifying NOx from being lost at start of the engine. Also, attention has been given to a technique of temporarily increasing the amount of fuel at start of an engine so that an exhaust-gas purification catalyst in which oxygen is captured will be reduced by being supplied with combustible components such as CO and HC at start of the engine.
In the case of various types of vehicles including: conventional vehicles, economy running vehicles, and hybrid vehicles, an engine is stopped by stopping the supply of fuel. However, even after the supply of fuel to the engine has been stopped, the engine keeps rotating idly a couple of times before coming to a complete halt. During such idle rotation of the engine, combustion chambers are supplied with only oxygen without being supplied with fuel. Accordingly, the exhaust-gas purification catalyst is supplied with oxygen and then captures it. Conventional vehicles, economy running vehicles, and hybrid vehicles are almost identical in that a catalyst captures oxygen as soon as an engine is stopped. However, in the case of economy running vehicles and hybrid vehicles, an engine is quite frequently stopped temporarily and then restarted. Therefore, it is far more crucial for economy running vehicles and hybrid vehicles than for conventional vehicles to suitably perform a reduction treatment of an exhaust-gas purification catalyst at start of an engine, namely, to temporarily increase the amount of fuel in order to sufficiently reduce the catalyst without allowing combustible components such as CO and HC to be discharged into the atmosphere.
In addition, economy running vehicles and hybrid vehicles encounter a problem peculiar to a temporary increase in the amount of fuel at start of an engine. In many gasoline engines that are designed to supply fuel by means of a carburetor or injection through ports, the problem is associated with a phenomenon in which part of supplied fuel adheres to the perimeter of intake ports and forms a liquid-fuel membrane. That is, while an engine that is designed to supply fuel by means of a carburetor or injection through ports is in operation, a liquid-fuel membrane of a substantially constant thickness is formed in the perimeter of intake ports. A considerable amount of fuel is used to form the liquid-fuel membrane.
Thus, the amount of fuel required for formation of the aforementioned liquid-fuel membrane must be taken into account in order to satisfactorily perform a reduction treatment of the exhaust-gas purification catalyst at start of the engine and temporarily increase the amount of fuel at start of the engine by an amount that is controlled to prevent combustible components of a surplus of fuel from being discharged into the atmosphere. Mostly in the case of conventional vehicles in which an engine is started only at takeoff, the aforementioned liquid-fuel membrane no longer exists at start of the engine. However, in many cases of economy running vehicles and hybrid vehicles in which an engine is stopped temporarily during traveling and restarted after a while, a liquid-fuel membrane substantially remains at start of the engine. In addition, the degree of residence of the liquid-fuel membrane differs depending on the length of elapsed time. If the increase in the amount of fuel at restart of the engine is always constant in such a case, the amount of added fuel that is introduced into combustion chambers fluctuates greatly. As a result, the amount of combustible components of fuel to be supplied to perform a reduction treatment of the exhaust-gas purification catalyst may become insufficient. Also, the atmospheric environment may be contaminated if combustible components of fuel are supplied in an excessive amount and discharged into the atmosphere.
It is an objective of the invention to provide a method of operating a vehicular internal combustion engine as an appropriate solution to the aforementioned problems which occur when the amount of fuel is increased at start of an engine. In order to achieve the aforementioned objective, a method of operating a vehicular internal combustion engine according to an aspect of the invention is designed such that an initial value of an increase in an amount of fuel at restart of the internal combustion engine is reduced from a predetermined standard value if a time that elapses from a timing when the internal combustion engine is started to a timing when the internal combustion engine is stopped temporarily is shorter than a predetermined value.
Further, an initial value of an increase in an amount of fuel at restart of the internal combustion engine is reduced from the predetermined standard value if an amount of air that flows through intake ports of the internal combustion engine from a timing when the internal combustion engine is started through a period in which the internal combustion engine is stopped temporarily is smaller than a predetermined value.
Furthermore, the amount of fuel at restart of the internal combustion engine is not increased if a time that elapses from a timing when the internal combustion engine is stopped to a timing when the internal combustion engine is restarted is shorter than a predetermined value.
If the increase in the amount of fuel at start of the engine is controlled on the basis of an estimated amount of fuel that has adhered to the perimeter of intake ports at start of the engine, the amount of fuel can be appropriately increased even in the case where the liquid-fuel membrane in the perimeter of the intake ports takes different states at start of the engine as in the case of economy running vehicles and hybrid vehicles and where the amount of fuel required for restoration of the liquid-fuel membrane may vary.